1. Field of the Disclosure
The present disclosure relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device and a driving method thereof which periodically switch between a negative polarity and positive polarity of data voltages. 2. Discussion of the Related Art
Flat panel display (FPD) devices are used in various electronic devices such as portable phones, tablet personal computers (PCs), notebook computers, etc. The FPD devices include liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting diode (OLED) display devices, etc. Recently, electrophoretic display (EPD) devices are being widely used as the FPD devices.
In the FPD devices, especially, LCD devices can be used in all electronic devices ranging from small devices to large devices, and thus are being widely used.
FIG. 1 is an exemplary diagram for describing a related art method of driving an LCD device, and shows waveforms of a common voltage Vcom, a data voltage Vdata, and a gate voltage Vgate.
LCD devices of the related art use various inversion systems such as a frame inversion system, a line inversion system, a column inversion system, and a dot inversion system, for preventing liquid crystal from being deteriorated when one-way electric field is applied to a liquid crystal cell for a long time.
In a case using the above-described inversion systems, data voltages Vdata outputted to respective data lines are switched from a negative polarity to a positive polarity or from the positive polarity to the negative polarity in units of a line or in units of a frame.
That is, the related art LCD devices repeat an operation in which data voltages Vdata are switched from a positive (+) polarity to a negative (−) polarity and then again switched from the negative (−) polarity to the positive (+) polarity, with respect to a common voltage Vcom.
For example, as shown in FIG. 1, a data voltage (Odd Line Vdata) outputted to an odd-numbered gate line is outputted as the positive (+) polarity during a first frame period, and then outputted as the negative (−) polarity during a second frame period.
In this case, a data voltage (Even Line Vdata) outputted to a line corresponding to an even-numbered gate line is outputted as the negative (−) polarity during the first frame period, and then outputted as the positive (+) polarity during the second frame period.
An inversion system, which outputs data voltages in this way, is generally called the line inversion system.
As described above, when a data voltage Vdata swings with respect to the common voltage Vcom, an input voltage Vdd higher by two times than a liquid crystal driving voltage is needed. Here, the liquid crystal driving voltage denotes a voltage which is required to output light by driving liquid crystal, and the input voltage Vdd denotes a voltage which is required to generate a data voltage Vdata substantially outputted to a data line for diving the liquid crystal.
For example, as shown in FIG. 1, when the liquid crystal driving voltage required to output a negative (−) data voltage or a positive (+) data voltage with respect to the common voltage is 8 V, it is required to supply the input voltage Vdd of 16 V to a data driver which outputs the data voltages, for alternately outputting the positive (+) data voltage and the negative (−) data voltage.
That is, although the liquid crystal driving voltage (a liquid crystal driving voltage (+) or a liquid crystal driving voltage (−)) substantially required to drive the liquid crystal is 8 V, as shown in FIG. 1, when data voltages swing, a difference voltage between a data voltage having the negative (−) polarity and a data voltage having the positive (+) polarity is 16 V, and thus, it is required to supply the input voltage Vdd of 16 V to a source driving IC that outputs the data voltages.
Therefore, in the related art LCD devices, when high-voltage driving is performed, the driving voltage Vdd increases by two times as the liquid crystal driving voltage increases.
When the liquid crystal driving voltage increase by 8 V, the input voltage Vdd increases by 16 V two times 8 V. Therefore, in an LCD device in which the liquid crystal driving voltage is set to 16 V (existing 8 V+8 V↑), the input voltage Vdd of 32 V (existing 16 V+16 V↑) is needed.
In this case, a related art source driving IC supported up to 16 V cannot be used, and a high-voltage source driving IC (S/D-IC) supported up to 32 V should be provided.
When it is assumed that a general high-voltage source driving IC (S/D-IC), which was developed in the past and is being used, uses 22 V as the input voltage Vdd, the maximum liquid crystal driving voltage “Vdd/2” drivable by the related art high-voltage source driving IC (S/D-IC) is “11V(existing 8V+3V↑)” (i.e., Vdd/2=11V(existing 8V+3V↑)). Therefore, in a case using the related art high-voltage source driving IC (S/D-IC), which is available when the maximum liquid crystal driving voltage is 11 V, the liquid crystal driving voltage can increase by only a maximum of 3 V with respect to the existing 8 V.
As LCD devices enlarge in size and become higher in definition, the liquid crystal driving voltage increases, and thus, the input voltage Vdd supplied to the source driving IC also increases.
However, since an input voltage applicable to the related art high-voltage source driving IC is limited, a new high-voltage source driving IC should be developed each time the liquid crystal driving voltage increases.
For this reason, the overall manufacturing cost of LCD devices increases inevitably, and source driving ICs which were previously used should be discarded.